JPH01222218A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To perform a white-and-black display by specifying the product of the layer thickness and optical anisotropy of nematic liquid crystal and providing the optical anisotropic body other than the nematic liquid crystal between a couple of polarizing plates. CONSTITUTION:This device is equipped with liquid crystal cells 2 and 6 formed by sandwiching the twist-oriented nematic liquid crystal between electrode substrates 3 and 4, and 7 and 8 which are arranged oppositely to each other and the couple of polarizing plates 1 and 10 which are arranged oppositely to each other across the liquid crystal cells 2 and 6, and the nematic liquid crystal is 120-330 deg. in twist angle. Here, the product DELTAn.d of the layer thickness (d) and optical anisotropy DELTAn of the nematic liquid crystal is 1.0-2.0. Then at least one optical anisotropic body is arranged between the couple of polarizing plates 1 and 10. Therefore, the hue at the time of selective voltage application is made black and that at the time of nonselection voltage application is made white. Consequently, the contrast is improved and there is no coloring, so this is adapted to VDT operation.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a liquid crystal display device. Liquid crystal display devices are widely used in portable computers and word processors as display devices that can be made thinner, lighter, and more power efficient.

[Prior Art J] As disclosed in Japanese Patent Laid-Open No. 60-50511, a conventional super twisted nematic type liquid crystal display device has a twist angle of liquid crystal molecules of 90 degrees or more, and has a pair of polarizing plates above and below a liquid crystal cell. and these polarization axes (absorption axes) and Tis
The included angle between the molecular axis direction of the liquid crystal molecules adjacent to the substrate is 3
It ranged from 0 degrees to 60 degrees. Therefore, the external hue of the liquid crystal cell when no voltage is applied is not white;
The color ranged from green to yellow-red. Furthermore, the external hue in the selective voltage application state was not black but blue. Therefore, it is very difficult to see and is not suitable for VDT work. Here, FIG. 3 shows the relationship between the directions of the polarization axes (absorption axes) of the liquid crystal cell and the polarizing plate of a conventional liquid crystal display device. In the figure, 22 is the rubbing direction of the upper electrode substrate of the liquid crystal cell, 23 is the rubbing direction of the lower electrode substrate of the liquid crystal cell, 24 is the method of the polarization axis (absorption axis) of the upper polarizing plate, 2
5 is the direction of the polarization axis (absorption axis) of the lower polarizing plate, 26 is the direction and angle of the twist angle of the liquid crystal molecules of the liquid crystal cell, the twist is from top to bottom, and 27 is the rubbing direction 22 of the lower electrode substrate. and the direction 24 of the polarization axis (absorption axis) of the upper polarizing plate, and 28 represents the angle between the rubbing direction 23 of the lower electrode substrate and the direction 25 of the polarization axis (absorption axis) of the lower polarizing plate. . In Figure 3, the angle 26 is about 200 degrees and the angle 27 is about 4 degrees.
FIG. 4 shows the spectrum of the appearance of the liquid crystal display device when the angle 28 is in the range of 0 degrees to 50 degrees, the angle 28 is in the range of 40 degrees to 50 degrees, and Δn-d of the liquid crystal is about 0.9 μm. In the same figure, curve ■ is a state in which no voltage is applied, and curve 1! is l
/ l OOd u t. The spectrum is shown in a state where a selective voltage is applied by y drive. [Problems to be Solved by the Invention] In the conventional technology, it is not possible to make the external hue of a liquid crystal display device white, and the hue ranges from green to yellowish red, which is psychologically difficult to accept as a display device. Ta. Furthermore, the hue upon application of the selection voltage was not black but a tone color, which was also not a desirable hue for a display device. SUMMARY OF THE INVENTION The present invention is intended to solve these problems, and its purpose is to provide a liquid crystal display device that can display black and white images. [Means for Solving the Problems J] The liquid crystal display device of the present invention comprises a liquid crystal cell formed by sandwiching twisted oriented nematic liquid crystal between two electrode substrates disposed facing each other, and a liquid crystal cell disposed on both sides with the liquid crystal cell sandwiched therebetween. The nematic liquid crystal has a twist angle of 120
In a liquid crystal display device having a range from 330 degrees to 330 degrees,
The product Δn−d of the thick layer d of the nematic liquid crystal and the optical anisotropy Δn of the nematic liquid crystal is in the range of 1.0 to 20, and there is at least one light beam between the pair of polarizing plates.
It is characterized by having an anisotropic body. [Function] In the liquid crystal display device of the present invention, the linearly polarized light that has passed through one of the pair of polarizing plates passes through the liquid crystal layer of the display liquid crystal cell and at least one optically anisotropic body, so that about 40
In the wavelength range from 0 nm to about 70 nm, the light becomes elliptically polarized light whose long axis direction is almost uniform. Because the long axes of elliptically polarized light are almost aligned, only a certain wavelength range will not be absorbed when it passes through the other polarizing plate.
Therefore, the light that passes through the polarizing plate can have a color close to white. However, if the twist angle of the liquid crystal in the display liquid crystal cell is less than 120 degrees, sufficient contrast cannot be obtained, and if it is greater than 330 degrees, the viewing angle tends to be narrow. [Example 1] FIG. 1 shows a cross-sectional view schematically showing the structure of the liquid crystal display device of the present invention. In FIG. 1, l is an upper polarizing plate;
2 is a liquid crystal cell (hereinafter referred to as the second cell) as an optically anisotropic body;
3 is the upper substrate of the second cell. 4 is the lower substrate of the second cell, 5 is the liquid crystal of the second cell, and 6 is the first liquid crystal cell (hereinafter referred to as the first liquid crystal cell) that performs display by applying a voltage.
7 is a lower electrode substrate of the first cell, 8 is a lower electrode substrate of the first cell, 9 is a liquid crystal of the first cell, and 10 is a lower polarizing plate. Here, the first cell and the second cell may be arranged upside down from the arrangement shown in FIG. 1. FIG. 2 is a diagram showing the relationship of each axis of the liquid crystal display device of the present invention6. The direction of the liquid crystal molecule axis in contact with the substrate will be hereinafter referred to as the rubbing direction. In the figure, 11 is the rubbing direction of the lower mold 4 substrate of the first cell, 1
2 is the rubbing direction of the upper side 7" substrate of the first cell, 13 is the rubbing direction of the lower substrate of the second cell, 14 is the rubbing direction of the upper substrate of the second cell, and 15 is the polarization axis of the lower polarizing plate (
16 is the polarization axis (absorption axis) of the upper polarizing plate
17 is the direction 1 of the polarization axis (absorption axis) of the upper polarizing plate.
6 and the rubbing direction 14 of the upper substrate of the second cell, 18 is the twist angle of the liquid crystal in the second cell, 19
20 is the angle formed by the rubbing direction 13 of the lower substrate of the second cell and the rubbing direction 12 of the upper electrode substrate of the first cell, and 20 is the angle formed by the rubbing direction 13 of the lower substrate of the second cell and the rubbing direction 12 of the upper electrode substrate of the first cell. The twist angle 21 of the liquid crystal in the cell is the angle between the rubbing direction 11 of the lower double positive substrate of the first cell and the direction 15 of the polarization axis (absorption axis) of the lower polarizing plate. Hereinafter, regarding the twist direction of the liquid crystal molecules in each cell, the left twist direction from the top to the bottom of the cell is assumed to be positive. Further, a state in which a large amount of transmitted light is produced by applying a non-selective voltage by l/1oOduLy driving is referred to as an OFF state, and a state in which a small amount of transmitted light is produced by applying a selective voltage is referred to as an ON state. Note that the present invention is not limited to 1/l 00 duty drive. Microhexane-based liquid crystals were used as the liquid crystals in the first and second cells, and ZLI-8 was used to achieve twisted orientation.
11 (manufactured by Merck), and CB-15 (manufactured by BDH) were used. The twist angle 20 of the liquid crystal of the first cell is approximately 200 degrees, Δn-d
is approximately 1.5 μm, angle 19 is approximately 90 degrees, and angle 17 is approximately 30 degrees.
The angle 21 is in the range from 30rx to 660 degrees, and the twist angle 18 of the liquid crystal of the second cell is set to 12 degrees.
Fig. 5 shows the spectral characteristics of the OFF state and ON state when 00 degrees and Δn-d is about 1.5 μm. In Fig. 5, curve ■ is in the OFF state, curve ! As is clear from Figure 5, in the OFF state, it shows high transmittance in each wavelength range, so it is white, and in the ON state, it shows low transmittance in each wavelength range, so it is black. It has become.

[Example 2] In Example 1, the twist angle 18 of the liquid crystal of the second cell is -1
00 degrees, Δn-d is approximately 1.0, and other conditions are as in Example 1.
In the same manner as in Example 1, a display closer to black could be obtained in the ON state than in Example 1. [Example 3J Similarly, in Example 1, the twist angle 18 of the liquid crystal of the second cell was set in the range of -400 degrees to +100 degrees, and Δn-d of the second cell was set in the range of 1.0 to 2.0. At the time, the shaded area in FIG. 6 was whiter in the OFF state and blacker in the ON state, confirming a desirable range. Here, the areas other than the hatched areas in FIG. 6 do not indicate areas that cannot be displayed. [Example 4] In Example 1, the twist angle 20 of the first liquid crystal was set to about 200.
If Δn-d of the first cell is approximately 2.0 μm, angle 19 is approximately 90 degrees, angle l is in the range of 30 degrees to 60 degrees, and angle 2I is in the range of 30 degrees to 60 degrees, then the second cell is When the torsion angle 18 and Δn-d are shown in the shaded area in Fig. 7,
It became whiter in the OFF state and blacker in the ON state. As mentioned above, the shaded area here is not an area that cannot be displayed, but is an area where the contrast is inferior to the shaded area. Therefore, when viewed as a display device, the shaded area is desirable. (Example 5) In Example 1, an l-axis polymer film made of polycarbonate was used instead of the second cell, and the Δ of the film was
nd was approximately 1.5 μm. At this time, the viewing angle became narrower, but it became white in the OFF state and black in the ON state. As the uniaxial polymer film, oriented films of DAC, PET, cellulose diacetate, PVA, polyamide, polyethersulfone, acrylic, polysulfone, polyimide, polyolefin, etc. can be used. [Example 6] In Example 1, an aluminum vapor-deposited film was provided under the lower polarizing plate 10 to obtain a reflective liquid crystal display device. In this case, a black and white display was similarly obtained. [Example 7] In Example 1, the twist angle 20 of the liquid crystal of the first cell was approximately 130 degrees, the Δn-d of the first cell was approximately 1°5 μm, and the angle 1
9 is about 90 degrees, angle 17 is from 30 degrees to 60 degrees, and angle 21 is from 30 degrees to 60 degrees. The twist angle 18 of the liquid crystal of the second cell was set to 1120 degrees, and Δn-d of the second cell was set to about 1.3 μm. Although the contrast was worse than in Example 1, a black and white display was obtained, resulting in a truly bright appearance. [Example 8] In Example 1, the twist angle 20 of the liquid crystal of the first cell was approximately 270 degrees, Δn-d was approximately 1.0 μm, and the angle lXl9 was approximately 9
0 degrees, angle 17 from 20 degrees to 50 degrees, angle 21 to 2
From 0 degrees to 50 degrees, the twist angle of the second cell's liquid crystal is 18 - 2
70 degrees, and Δn-d was approximately 10. A black and white display is obtained,
Furthermore, the contrast was improved compared to Example 1. [Example 9] In Example 5, two uniaxial polymer films with Δn-d of about 0.8 μm were stacked. Similar results to Example 5 were obtained. [Example +03 The angle between the two films used in Example 9 in the axial direction was 3
It was set so that it was 0 degrees. As a result, the contrast was improved compared to Example 9. [Example 11] In Example 1, a cholesteric film was used instead of the second cell. Then, the appearance became white. (Example 12) In Example 1, a purple color polarizing plate was used instead of the gray type for the upper polarizing plate l.As a result, the appearance became whiter and brighter. [Effects of the invention] As described below. According to the present invention, the hue when two selection voltages are applied can be made black, and the hue when non-selection voltages are applied can be made white.This improves the contrast, and since there is no coloration, it is suitable for VDT work.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view illustrating the structure of the liquid crystal display device of the present invention as a model. In the figure, l is the upper polarizing plate, 2 is the second
3 is the upper substrate of the second cell, 4 is the lower substrate of the second cell, 5 is the liquid crystal of the second cell, 6 is the first cell, 7 is the upper doublet substrate of the first cell, 8 is the first cell 9 is the liquid crystal of the first cell, and 10 is the polarizing plate on the first side. FIG. 2 is a diagram showing the relationship between each axis of the liquid crystal display device of the present invention. In the same figure, 11 is FlIII of the first cell.
12 is the rubbing direction of the G-side electrode substrate of the first cell, 13 is the rubbing direction of the lower substrate of the second cell, 14 is the rubbing direction of the upper substrate of the second cell,
15 is the direction of the polarization axis (absorption axis) of the lower polarizing plate, 16 is the direction of the polarization axis (absorption axis) of the upper polarizing plate, and 17 is the direction of the polarization axis (absorption axis) of the upper polarizing plate and the direction of the second cell. 18 is the angle formed by the rubbing direction of the upper substrate, 18 is the size of the twist angle of the liquid crystal molecules of the second cell, and 19 is the angle between the rubbing direction of the lower substrate of the second cell and the rubbing direction of the upper double positive substrate of the first cell. The angle 20 is the size of the twist angle of the liquid crystal molecules in the first cell,
21 indicates the angle between the rubbing direction of the lower double Yang substrate of the first cell and the polarization axis (absorption axis) of the lower polarizing plate. FIG. 3 is a diagram showing the relationship between each axis of a conventional liquid crystal display device. FIG. 4 is a diagram showing the relationship between wavelength and transmitted light intensity in a conventional liquid crystal display device. FIG. 5 is a diagram showing the relationship between wavelength and transmitted light intensity in the liquid crystal display device of the present invention. FIG. 6 is a diagram showing the relationship between the first cell and the second cell in the embodiment of the present invention. FIG. 7 is a diagram showing the relationship between the first cell and the second cell in the embodiment of the present invention. Applicant: Seiko Epson Corporation Figure 1 Figure 2 ψ Figure 3 Length Figure 4 (%) Figure 5 1 r= ILfl needle ist, t Zoo degree Figure 6

Claims (1)

[Claims] A liquid crystal cell has a twisted oriented nematic liquid crystal sandwiched between two opposing electrode substrates, and a pair of polarizing plates are arranged on both sides of the liquid crystal cell, and the nematic liquid crystal is twisted. In a liquid crystal display device having an angle in the range of 120 degrees to 330 degrees, the product Δ of the layer thickness d of the nematic liquid crystal and the optical anisotropy Δn of the nematic liquid crystal
A liquid crystal display device characterized in that n·d has a range of 1.0 to 2.0, and at least one optically anisotropic body other than the nematic liquid crystal is provided between the pair of polarizing plates.